Molecular Perturbation Model for the Spin–Lattice Coupling Coefficients of 6 A 1 States to E θ Strains

The proposed perturbation model involves second‐order molecular spin–orbit interactions between the fundamental state 6 A 1 , and the components of orbital triplets 4 T 1 and 6 T 1 , calculated in symmetry D 2d induced by E‐strains. The matrix elements of the molecular spin–orbit interactions are first calculated for the states 4 T 1 and 6 T 1 defined from multielectronic configurations with three open shells. Then, it is shown that the second‐order molecular spin–orbit perturbation involving these states 4 T 1 and 6 T 1 is strictly zero if these states are degenerate. Finally, it is shown that the most important contribution is due to the three states 4 T 1 , defined from multielectronic configurations with two open shells.